Self-interacting dark matter

In astrophysics and particle physics, self-interacting dark matter (SIDM) assumes dark matter has self-interactions, in contrast to the collisionless dark matter assumed by the Lambda-CDM model. SIDM was postulated in 2000 to resolve a number of conflicts between observations and N-body simulations (of cold collisionless dark matter only) on the galactic scale and smaller.[1][2] It was also used to explain the 2015 observations of ESO 146-5 in the core of the Abell 3827 galaxy cluster.[3] However, the latter finding has since been discounted based on further observations and modelling of the cluster.[4][5]

If the self-interacting dark matter is in hydrostatic equilibrium, its pressure and density follow:

${\displaystyle \nabla P_{\chi }/\rho _{\chi }=\nabla \Phi _{\rm {tot}}=\nabla (\Phi _{\chi }+\Phi _{b})}$

where ${\displaystyle \Phi _{\chi }}$ and ${\displaystyle \Phi _{b}}$ are the gravitational potential of the dark matter and a baryon respectively. The equation naturally correlates the dark matter distribution to that of the baryonic matter distribution. With this correlation, the self-interacting dark matter can explain phenomena such as the Tully-Fisher relation.

Self-interacting dark matter has also been postulated as an explanation for the DAMA annual modulation signal.[6][7][3]